Spreading the message about its work with disadvantaged young people.
Martina Milburn has been in charge of the Prince's Trust for 17 months and has yet to perfect one of her most basic tasks. "I'm still learning how to curtsy properly," she confesses. "I'm 47 now and I think my legs are too old to ever be great at it."
Of course, it never occurred to Milburn in 1976, when she took her first job as a cub reporter, that she should prepare for the day when she would be working alongside the heir to the throne.
These days her mobile frequently chimes to Charles's calls, although his is not the first voice she hears. "Usually his private secretary calls and says 'the prince is on the phone; can you speak to him?'" she says.
The calls have been more regular of late. "I've seen him five times in the past month," she adds.
Talking shop with Prince Charles sounds like a surreal working relationship, yet Milburn's career path is full of quirky turns. She started out as the first woman on the Press Association's journalist training scheme, but eventually left Fleet Street - her last story exposed baby selling in Peru.
She was tempted away from the media world when fellow journalist Peter Stanford invited her to see a charity he chaired called Aspire, which helps people with spinal cord injuries. The next thing she knew she was chief executive. "I'm passionate about social justice," she says. "I'd written about the third world for 10 years and thought I ought to do something for my own community."
When she applied to succeed Tom Shebbeare at the Prince's Trust, Charles sat in on her interview. "He had the final say on whether I got the job and I was very nervous," she says.
The trust was set up in 1976, the same year Milburn's career began, yet three decades later the organisation remains a bit of a mystery.
"Everybody has heard of it but nobody actually knows what it does," she says. It has helped half a million disadvantaged 14 to 30-year-olds, but that tends to get lost amid the froth about Charles and the charity's high-profile events, such as Party in the Park. Milburn, however, is sick of talking numbers. "I don't care if we take 40,000 through the programme or 35,000 next year," she says. "We have to look more at the outcomes than at the outputs."
Maybe it's convenient to talk down figures given that the charity's income fell from £55.3m to £53.8m last year. "Any chief executive is concerned when income is going down, but if you look at the past five or six years it's stayed at around £50m," she says.
Nevertheless, her goal is to maintain rather than increase income, and she admits: "The biggest challenge now is to do with funding. The trust does not fit neatly into any obvious government programme or department.
Our projects often straddle several departments."
Labour's plan to devolve funding through local area agreements is also troublesome. "Where we had one single contract before - now we have nine or ten," she says.
Milburn sees next year's 30th anniversary celebrations as a chance to stimulate individual giving and become less dependent on statutory funding. "It's a chance to get the trust better known for what it does," she says.
Princes William and Harry recently got involved for the first time, but it seems no one has discussed succession planning with the Windsors. When Charles becomes king, will the Prince's Trust become the King's Trust or will Charles's sons take over? Milburn doesn't know.
She does know, however, that she won't blab about her off-the-record royal encounters. "There will be no book or diary," she says. "One of the worst things you can do is betray someone on that level."